Light Intensity Investigation

by jackbardsleystudentscotchwaedu (student)

Science Light Intensity Investigation

PROBLEM/RESEARCH QUESTION

In this investigation, a controlled experiment will be conducted to determine whether the distance between an object and a light source has an effect on the intensity of light and if so, do the illuminance increase or decrease as the distance from the light source increases. Research will be formulated by conducting a controlled experiment in which we will observe the intensity of light received by a light sensor at various distances and evaluate the results gathered to determine the relationship between light intensity and distance. This phenomenon can be experienced when an oncoming car has it head lights switched on, the light intensity seems to increase as the car approaches. Similarly, the rate of photosynthesis also relies heavily on the intensity of light, as the process is seemed to be quicker when the sun’s light intensity is strong. Thus, the relationship between light intensity and distance is important to investigate so that experimental reasoning can be deducted for these phenomena’s. The intensity of the light is the amount of light that falls on a specific object. This measure is called illuminations and is expressed in Lux when the distance is measured in metric terms. A lux equals one lumen per square metre. (Anderson, 2009)

HYPOTHESIS

Increasing the distance of the light sensor from the light source will decrease the intensity of light (or luminance) detected by the sensor. This hypothesis is based on the knowledge that as light waves travel out from a light source in straight lines, they spread out and become less concentrated as they travel further away- making it appear dimmer. Furthermore, when an object is placed near a source, majority of the light waves emitted are concentrated on it, however when placed further back, only a small proportion of the waves are hitting it. Due to this, increasing distance ultimately decreases the illuminance (how much light from a source hits a specific object) and thus, the light intensity.

VARIABLES

The independent variable (the variable being changed): The independent variable is going to be the distance between the light sensor and the light source (cm) with measurements varying from 10cm-100cm and increasing at 10cm increments. We will do this in order to see the effects varying distance has on light intensity. The variable will be altered by increasing the distance between the two objects by 10cm (interval length) for each set of trials. We will measure and change this gap by using a metre ruler to determine the exact distance and then we will place the light source at one end and the sensor at the determined mark on the ruler.

The dependent variable (the variable being measured): The dependent variable is going to be the intensity of light illuminated by the light source at each particular distance (ranging from 10cm-100cm). This variable will be measured in the unit of measurement LUX. To determine the LUX illuminated at various distances, we will use Data Studio to give us accurate measurements of light hitting the light sensor that will be located at one of the ten distances, thus giving us our measurement for the particular trial.

The control variables (the variables kept the same): The other variables, which we need to keep constant, are:

The same conditions present around the experiment (room temperature, background light, disturbance, etc.). To ensure that the experiment is fair, we will minimize any background disturbance by conducting the experiment in a secluded area away from other groups. We will also close all blinds and switch off the room light so that there is little to no background light interfering with the light sensor’s readings. This is essential for the data’s reliability as background light can affect the readings by increasing the light intensity (lux) picked up by the sensor- more than what is being emitted by the light bulb.
The same strength of light being emitted from the light bulb (12 volts). To control this variable we will ensure that the tuner on the ray box is at the 12-volt (the highest) mark for all trials.
The same length of time each trial is conducted for (30 seconds). To keep this variable constant, we will use the clock on data studio to measure the time from the time we click the start button. The trial will finish when the virtual stopwatch reaches the 30sec mark and the stop button is clicked.
The same height of the light sensor above the desk. This will be controlled by using the same wooden block to place the sensor, thus ensuring that there are no changes in height of the wooden block and as a result, the light sensor.
The same light mode chosen on the sensor. To control this, we will choose the sunlight mode on the light sensor and ensure that it is not changed to either of the other two buttons.
The same light source used. The same light bulb will be used in each trial and not changed throughout the experiment.
The same nozzle on the light sensor used to detect light-the front nozzle. To control this, we will place the sensor parallel to the ruler so that the front nozzle faces directly towards the light bulb and the side nozzle faces away. This is essential to ensure that we achieve accuracy as using two different nozzles would alter results as they have different levels of detecting light intensity with the side nozzle usually showing the light intensity to be significantly lower than the front nozzle.
The same person handling the light sensor during the experiment. Identifying one group member to handle the sensor before the experiment and then ensuring that he only handles it during each trial will control this variable.

ALL EQUIPMENT IS TO BE KEPT CONSTANT TROUGHT THE EXPERIMENT TO OBTAIN CONSISTENTSY

EXPERIMENTAL PLAN

Materials/Equipment:

1x 12v Light Source (or Ray Box)
1x 25cm2 Wooden Block
1x 25cm2 Square White Cardboard
1x Light Sensor
1x 1metre Ruler
1x USB Link
1x Laptop
1x Power Supply Box
1x Desk
1x DC Transformer

Setup & Plan:

Here are the details of how we will conduct our experiment and the measurements we will make and process:

Our group will measure the light ...

This is a preview of the whole essay

ALL EQUIPMENT IS TO BE KEPT CONSTANT TROUGHT THE EXPERIMENT TO OBTAIN CONSISTENTSY

EXPERIMENTAL PLAN

Materials/Equipment:

1x 12v Light Source (or Ray Box)
1x 25cm2 Wooden Block
1x 25cm2 Square White Cardboard
1x Light Sensor
1x 1metre Ruler
1x USB Link
1x Laptop
1x Power Supply Box
1x Desk
1x DC Transformer

Setup & Plan:

Here are the details of how we will conduct our experiment and the measurements we will make and process:

Our group will measure the light intensity at various distances by using the application Data Studio to provide us with our readings. The readings that the light sensor receives will show up on our laptops and will be the basis for our data that will be measured in the unit LUX. Averages for each distance will be calculated by applying a simple formula where all three trials are added up, before the total is divided by three, leaving us with our average for that particular distance.

After our data has been collected using the above method and formed into a table, we will process and convert it into a marked scatter graph with a “line of best fit”, which in this case will be a power trend-line. Our experiment will be set up (like in the above image) with the light source at one end of the desk so that we can get data for distances as great as 100cm.

Some techniques we could use to achieve prime accuracy and precision are:

Moving the light sensor sideways along the block during each trial to ensure that we get it directly in line with the light bulb so that our highest reading is the highest possible for that distance.
Comparing our results with another group to see if there are any anomalies in our data.

Method:

Collect all necessary equipment and plug in the light source (or ray box) into the DC transformer and then the transformer into a power point.
Set the power tuner to 12 volts (maximum) and place at one end of the desk with the bulb facing inwards.
Place the ruler directly in front of the light source so that one end (marked 0cm) is almost in line with the light bulb. This is so that the centimetre markings on the ruler are the actual distance from the light source.
Attach the USB link to the light sensor (as shown in the image on the right) and then plug the USB link into the laptop.
Open Data Studio on your laptop, making sure that the connection between the application and the light sensor is strong. Once done, press the sunlight button on the light sensor and hold until it turns yellow.
Slide the white cardboard sheet into the back of the light source and shut the flaps on the sides so that light escaping out the back and sides is minimized. Make sure all other lights have been turned off and natural light has been minimized as well, making sure it stays the same for all trials.
Place the wooden block next to the 10cm mark on the ruler, ensuring that it is directly in line with the front side of the light source.
Set the light sensor on top of the block ensuring that the front nozzle faces towards the light source and the tip is also in line with the 10cm mark on the ruler. Complete a few pre-tests to ensure that everything is working smoothly.
Press and hold the start button on data studio for 60 seconds and record the highest reading that appears in the data box. Record this reading in your table as a valid trial for the distance of 10cm.
Repeat the above step twice, ensuring that only the highest reading is recorded for each of the two remaining trials. Ensure that the control variables are the same as they were for the trial before with outside interference minimized so that the illuminated light measurements (the dependent variable) are as accurate as possible.
Move on to the next distance (20cm) and repeat steps 7-10, ensuring that the light sensor is at the new measurement. Once done, repeat 7-10 for the remaining eight distances and record data in table.
Once finished, eject the USB link from the laptop, save data on data studio and return equipment.
Write up report, ensuring to include a graph and results table.

*NOTE: Capture pictures throughout experiment with the laptop and remember to write down all observations.

RESULTS

Results Table:

DATA PROCESSING

Graph: I think the best kind of graph to use to display these results would be to create a line graph:

DISCUSSION

Our results show a wide range of relationships between the data. For instance, the shape of our graph shows an inverse relationship between light intensity and distance. The power trend line displays this relationship as it shows that as the distance increase, the light intensity decreases through its angular line curving downwards from left to right. The graph also suggests that if further distances were to be measured, the trend in decreasing readings will continue, as so far there has been no change in the inverse relationship.

There was no real pattern in the decreasing rate of light intensity against distance as the power trend line on the graph displays different gradients between points (i.e. the gradient between 10-20cm is much greater than that between 80-90cm). This is backed up by the fact that the equation formulated for the data- y=161484x-1.1661- which, although is a non-linear equation/relationship, it is complex and does not suggest a definite pattern and would most likely change if another distance was added. The data looks fairly reliable, as there are no anomalies, although the equation formulated does not match with the inverse square law (mentioned in conclusion), suggesting minor inaccuracy in data.

CONCLUSION

In conclusion, the results gathered are sufficient and clearly show that the distance an object is placed away from a light source does have an effect on the intensity of light (or illuminance) hitting a specific object. Furthermore, the data also allows for us to establish the relationship that the further the distance, the lower the illuminance. This convincingly answers our research question and proves my hypothesis correct/valid as the 10cm distance trials proved to obtain the highest light intensity (as hypothesized) at an average of 2614.33 Lux and the lowest readings were detected at the 100cm distance. Also, at each trial the readings were lower than those measured in all of the distances shorter than it. This is backed up by the sufficient data plotted on the graph that shows a steady decline in LUX measurements from 2613.33lux to 56.88lux.

The relationship between light intensity and distance occurs because light waves are emitted evenly in straight lines, they illuminate a specific area and as they travel further, they spread out and get less concentrated as the same amount of light has to cover more area, therefore decreasing the intensity of light. As a result, the brightness is also decreased, making the light look dimmer. This theory is the base principle for the inverse square law, which is a law in physics that can be used to find the intensity of light at any given distance by using the above knowledge. The law states that the intensity of light at a given point equals the inverse of the distance squared multiplied by the original intensity of light at source (shown in figure 1). For example, if the distance is two units the light intensity will be one fourth of the original intensity, as the concentration of light would have decreased, as more area would be there to cover. (Britannica, 2005)

EVALUATION

Our experiment went quite well and we were able to collect all the necessary readings required, encountering very few problems during the experiment and were able to conduct three trials for each distance, thus improving the reliability of our data and deeming the experiment fair and valid. We had a sufficient sample size of ten different distances at equal intervals of 10cm-adequete for this experiment. The extensive range of data collected allowed us to obtain an accurate trend line and formulate justifiable conclusions. Using our results, we were able to answer our research question in the affirmative that the distance of an object from a light source does affect the light intensity or illumines hitting the object, with the relationship being that an increase in distance equates to a decrease in light intensity.

The only major problem that we encountered and could have affected the reliability of our data was that we were unable to completely block out the background light coming in through the windows. Although one of the control variables was that all background light would be controlled and minimized largely, we were unable to compile with this as the blinds still let majority of the sun light in. We also did not account for the light emitted from the light bulbs used by other groups during their trials- illuminated light that was potentially detected by our light sensor. We attempted to solve this problem by using sheets of paper to make a rectangular dome around the set up. This somewhat controlled the impact of background light, however it was not able to completely as the paper was only able to dim and reduce the intensity of light passing through into the set up and consequently, to the light sensor. This problem had a minor affect on the reliability of our data, although not enough to determine the test invalid, as we were still able to establish a relationship between distance and light intensity with reasonably accurate data that was otherwise reliable as no other problems were experienced.

Our method was fairly clear, concise and allowed us collect our data in a fairly orderly way, doing so for most tests. It allowed us to complete the experiment with accuracy excluding the human errors present that occur in most experiments and the major problem (mentioned above) that were inevitable based on the way the experiment was conducted. Although our method and experimental plan were quite accurate, easy to understand and allowed us to achieve our target of determining a relationship through a small-scale experiment, there are still many improvements that could be made to it to improve the validity of our results and further experiments could be carried out to extend this investigation. These include:

Completely eliminating the background light by conducting the experiment in a dark room with no other light source other than the 12volt light bulb so that reliability is improved.
Using shorter intervals between distances (i.e. 5cm) so that our rule (y = 161484x-1.661) will be more accurate with a larger sample size.
Positioning the light sensor at various heights and angles so that we can investigate how light waves travel and in which direction the intensity is at its greatest.
Using different types of light (infrared, ultraviolet, etc.) to investigate which type has the highest frequency.

Bibliography

Anderson, L. (2009). Intensity of Light . Retrieved February 18, 2014, from Encyclopedia Britannica: http://school.eb.com.au/levels/middle/article/275471#203834.toc

Britannica. (2005). Measuring Light. Retrieved February 18, 2014, from Encyclopedia Britannica: http://school.eb.com.au/levels/middle/article/275471#203834.toc

Nave, R. (2011). Inverse Square Law. Retrieved February 19, 2014, from Hyper Physics: http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html